JP2004047916A - Compound thin film solar battery and its manufacturing method - Google Patents

Compound thin film solar battery and its manufacturing method Download PDF

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JP2004047916A
JP2004047916A JP2002237158A JP2002237158A JP2004047916A JP 2004047916 A JP2004047916 A JP 2004047916A JP 2002237158 A JP2002237158 A JP 2002237158A JP 2002237158 A JP2002237158 A JP 2002237158A JP 2004047916 A JP2004047916 A JP 2004047916A
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aqueous solution
buffer layer
absorbing layer
film
film solar
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JP4264801B2 (en
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Satoshi Shiozaki
塩崎　諭
Masashi Aoki
青木　誠志
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Honda Motor Co Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/541—CuInSe2 material PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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Abstract

<P>PROBLEM TO BE SOLVED: To provide an n-type buffer layer for the hetero-junction of an excellent joining property and stable characteristics on a light absorbing layer composed of a p-type compound semiconductor. <P>SOLUTION: In the manufacturing method of a compound thin film solar battery composed by providing the n-type buffer layer for the hetero-junction on the light absorbing layer composed of the p-type compound semiconductor formed on a back surface electrode, at the time of forming the buffer layer by a CBD method using a 3-liquid mixed solution of zinc sulfide ZnSO4, thiourea CS(NH2)2 and ammonia NH4OH, the light absorbing layer is immersed in the 3-liquid mixed solution and the mixing ratio of the solution is changed so as to easily generate a component of ZnO from ZnS as the reaction of film formation advances. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【産業上の利用分野】
本発明は、裏面電極上に形成されたｐ型化合物半導体からなる光吸収層の上にヘテロ接合のためのｎ型のバッファ層を設けてなる化合物薄膜太陽電池およびその製造方法に関する。
【０００２】
【従来の技術】
図１は、一般的な化合物半導体による薄膜太陽電池の基本構造を示している。それは、ＳＬＧ（ソーダライムガラス）基板１上に裏面電極（プラス電極）となるＭｏ電極２が成膜され、そのＭｏ電極２上にｐ型の光吸収層５が成膜され、その光吸収層５上にヘテロ接合のためのｎ型のバッファ層６を介して透明電極（マイナス電極）７が成膜されている。
【０００３】
その化合物半導体による薄膜太陽電池における光吸収層５としては、現在１８％を超す高いエネルギー変換効率が得られるものとして、Ｃｕ，（Ｉｎ，Ｇａ），ＳｅをベースとしたＩ−ＩＩＩ−ＶＩ２族系のＣｕ（Ｉｎ＋Ｇａ）Ｓｅ２によるＣＩＧＳ薄膜が用いられている。
【０００４】
従来、この種の化合物薄膜太陽電池におけるバッファ層として、ＣＢＤ（ケミカルバスデポジション）法によって、溶液から化学的にＩＩ−ＶＩ族化合物半導体であるＣｄＳ膜を成長させることにより、ＣＩＳ光吸収層と最適なヘテロ接合を得ることができるようにしている（米国特許第４６１１０９１号明細書参照）。
【０００５】
また、従来、有害物質であるＣｄを含まない高い変換効率のヘテロ結合を得ることができるバッファ層として、ＣＢＤ法によってＺｎＳ膜を形成させるようにしたものがある（特開平８−３３０６１４号公報参照）。
【０００６】
【発明が解決しようとする課題】
解決しようとする問題点は、従来の化合物薄膜太陽電池では、ｐ型化合物半導体である光吸収層とｎ型半導体であるバッファ層の組成が全く異なるために、その接合に欠陥が生じやすいものになっていることである。
【０００７】
また、ＣＢＤ法によってバッファ層を成膜させるに際して、溶液に光吸収層を浸すと光吸収層へのＺｎまたはＣｄ成分の拡散とＺｎＳまたはＣｄＳの成膜とが同時に進行するので、光吸収層の結晶性やその表面状態によって特性のバラツキを生じやすいものになってしまうという問題がある。
【０００８】
【課題を解決するための手段】
本発明は、裏面電極上に形成されたｐ型化合物半導体からなる光吸収層の上にヘテロ接合のためのｎ型のバッファ層を設けてなる化合物薄膜太陽電池の製造方法にあって、硫化亜鉛ＺｎＳＯ４、チオ尿素ＣＳ（ＮＨ２）２、アンモニアＮＨ４ＯＨの３液混合水溶液を用いてＣＢＤ法によりバッファ層を形成するに際して、接合性の良い特性の安定したｐｎ接合を得ることができるようにするべく、その３液混合水溶液に光吸収層を浸して成膜の反応が進むにしたがってＺｎＳからＺｎＯの成分が生じやすくなるように水溶液の混合比を変えていく処理手段をとるようにしている。
【０００９】
また、本発明は、裏面電極上に形成されたｐ型化合物半導体からなる光吸収層の上にヘテロ接合のためのｎ型のバッファ層を設けてなる化合物薄膜太陽電池において、下部の光吸収層から上部の透明電極へ向かって成分の割合がＺｎＳからＺｎＯに連続的または段階的に変化するバッファ層を設けるようにしている。
【００１０】
【実施例】
図２および図３は、化合物薄膜太陽電池の製造過程を示している。
【００１１】
まず、図２に示すように、ＳＬＧ（ソーダライムガラス）基板１上に裏面電極としてのＭｏ電極２をスパッタリングにより成膜する。次いで、そのＭｏ電極２上にＣＩＧＳ薄膜による光吸収層５を作製するに際して、先にＩｎ単体ターゲットＴ１を用いた第１のスパッタ工程ＳＰＴ−１によってＩｎ層３２を成膜したうえで、その上に、Ｃｕ−Ｇａの合金ターゲットＴ２を用いた第２のスパッタ工程ＳＰＴ−２によってＣｕ−Ｇａ合金層３１を成膜して、Ｉｎ層３２およびＣｕ−Ｇａ合金層３１からなる積層プリカーサ３を形成する。そして、熱処理工程ＨＥＡＴにおいて、その積層プリカーサ３をＳｅ雰囲気中で熱処理することにより、ＣＩＧＳ薄膜による光吸収層５を作製する。
【００１２】
このように、Ｍｏ電極２上にＩｎ層３２を設けたうえで、その上にＣｕ−Ｇａ合金層３１を設けて積層プリカーサ３を形成するようにしているので、Ｍｏ電極２との界面における元素の固層拡散による合金化を抑制することができる。そして、その積層プリカーサ３をＳｅ雰囲気中で熱処理してセレン化する際に、Ｍｏ電極２側にＩｎ成分を充分に拡散させることができるとともに、拡散速度の遅いＧａがＭｏ電極２との界面に偏析して結晶性の悪いＣｕ−Ｇａ−Ｓｅ層が形成されることがないようにして、均一な結晶による高品質なＰ型半導体のＣｕ（Ｉｎ＋Ｇａ）Ｓｅ２によるＣＩＧＳの光吸収層５を作製することができる。
【００１３】
したがって、Ｍｏ電極２との界面に、結晶性が悪くて構造的に脆く、かつ導電性を有する異層（Ｃｕ−Ｇａ−Ｓｅ層）が偏析するようなことがなくなり、Ｍｏ電極２との密着性が高くて構造的に強固な、しかもセル間でリークをきたして電池特性が劣化することのない品質の良い光吸収層を得ることができるようになる。
【００１４】
次に、図３に示すように、ｐ型の光吸収層５とのヘテロ接合をとるためにｎ型のバッファ層６を形成する。そして、そのバッファ層６上にＺｎＯ：Ａｌ，ＴＣＯなどからなる透明電極７をスパッタリングにより成膜する。
【００１５】
図４および図５は、化合物薄膜太陽電池の他の製造過程を示している。
【００１６】
この場合には、積層プリカーサ３のセレン化の熱処理時に、Ｎａ成分が光吸収層５に拡散して光電変換効率を向上させることができるように、Ｍｏ電極２上にＮａ２Ｓからなるアルカリ層８を設けるようにしている。
【００１７】
そのアルカル層８は、例えばＮａ２Ｓ・９Ｈ２Ｏ（硫化ナトリウム９水和物）を重量濃度０．１〜５％で純水に溶かした水溶液にＭｏ電極２の成膜基板を浸して、スピンドライ乾燥させたのち、膜中残留水分の調整のために、大気中１５０℃で６０分間のベーク処理を行うことによって形成する。
【００１８】
そして、ＳＬＧ基板１とＭｏ電極２との間に、ＳＬＧ基板１に含まれるＮａ成分が光吸収層５に拡散するのを制御するＳｉＯ２，Ａｌ２Ｏ３などからなる拡散制御層９をＣＶＤ法によって形成するようにしている。
【００１９】
本発明は、このような構成による化合物薄膜太陽電池にあって、特にバッファ層６として、下部の光吸収層５から上部の透明電極７へ向かって成分の割合がＺｎＳからＺｎＯに連続的または段階的に変化する構造のものとしている。
【００２０】
また、本発明では、バッファ層６を形成するに際して、硫化亜鉛ＺｎＳＯ４、チオ尿素ＣＳ（ＮＨ２）２、アンモニアＮＨ４ＯＨの３液混合水溶液を用いたＣＢＤ法を採用して、その３液混合水溶液に光吸収層５の表面を浸して成膜の反応が進むにしたがってＺｎＳからＺｎＯの成分が生じやすくなるように水溶液の混合比を変えていく方法をとるようにしている。
【００２１】
その際、チオ尿素の混入量が他の２液よりも少ない３液混合水溶液に光吸収層５の表面を浸して成膜を行わせたうえで、その水溶液における硫化亜鉛の混入量を連続的または段階的に増加させながら成膜を継続して行わせるようにしている。
【００２２】
そして、成膜中、水溶液を加熱してアンモニアを蒸発させるようにしている。
【００２３】
通常では、０．１６Ｍ＿ＺｎＳＯ４、０．６Ｍ＿ＣＳ（ＮＨ２）２、７．５Ｍ＿ＮＨ４ＯＨの各水溶液を等量ずつ混合し、その３液混合水溶液中にＳＬＧ基板１上にＭｏ電極２および光吸収層５が形成された基材を投入したうえで、アンモニアの揮発を抑制するために容器に蓋をして、３０〜１２０分間浸漬してバッファ層６の成膜を行わせるようにしている。
【００２４】
それに対して、本発明では、上記の３液混合水溶液中に基材を投入してバッファ層６の成膜を行わせるに際して、当初はチオ尿素の量を減らしてアンモニアを蒸発させながら成膜を行わせ、反応が進むにしたがってＺｎの供給源を増加させるべくＺｎＳＯ４を追加していくことにより、３液混合水溶液をＺｎ（ＯＨ）２が生じやすい組成になるように連続的または段階的に変えるようにしている。
【００２５】
その具体的なＣＢＤ法によるバッファ層６の成膜としては、以下のとおりである。
【００２６】
第１段階の処理として、０．１６Ｍ＿ＺｎＳＯ４、０．６Ｍ＿ＣＳ（ＮＨ２）２、７．５Ｍ＿ＮＨ４ＯＨの各水溶液を２４０ｍｌ：１６０ｍｌ：２４０ｍｌの割合で混合して、８０℃のウォータバスにて２０分間加熱したのちに、その３液混合水溶液中に基材を投入して、１５分間の成膜を行わせる。
【００２７】
第２段階の処理として、第１段階の３液混合水溶液にＺｎＳＯ４・７Ｈ２Ｏを３．６８ｇ（０．１６Ｍ換算で８０ｍｌ）を加えて、１５分間の成膜を行わせる。
【００２８】
第３段階の処理として、第２段階の３液混合水溶液にさらにＺｎＳＯ４・７Ｈ２Ｏを１．７６ｇを加えて、１５分間の成膜を行わせる。
【００２９】
第４段階の処理として、第３段階の３液混合水溶液にさらにＺｎＳＯ４・７Ｈ２Ｏを１．７６ｇを加えて、１５分間の成膜を行わせる。
【００３０】
第５段階の処理として、第１段階から第４段階の処理による合計６０分間の成膜を行ったのち、Ｚｎ（ＯＨ）２の脱水を行ってＺｎＯを得るべく、１００〜３００℃の温度で３０〜３００分のあいだ加熱するアニール処理を行う。
【００３１】
成膜中は、アンモニアを揮発させてよりＺｎ（ＯＨ）２が生成しやすいようにするために、３液混合水溶液の容器に蓋をしないで、開放状態で基材の浸漬を行わせる。
【００３２】
ＣＢＤによる化学反応としては、最初に、
ＺｎＳＯ４＋ｘＮＨ４ＯＨ→〔Ｚｎ（ＮＨ３）ｘ〕２＋ＳＯ４２＋ｘＨ２Ｏ
ＺｎＳＯ４＋２ＮＨ４ＯＨ→Ｚｎ（ＯＨ）２↓＋２ＮＨ４＋ＳＯ４２
の競争反応が起こる。この反応により生じたＺｎのアンミン錯体がチオ尿素と反応してＺｎＳが生ずるが、アンモニアの濃度（ペーハーを含む）および３液混合水溶液の各成分の比率などによってその反応の起こりやすさを制御することが可能であると考えられる。
【００３３】
このように、本発明によれば、バッファ層６の成分の割合が、下部の光吸収層５から上部の透明電極７へ向かってＺｎＳからＺｎＯに徐々に変化することになる。したがって、光吸収層５に対して接合性の良い特性の安定した高品質なｐｎ接合を得ることができるようになる。そして、透明電極７との間の障壁をなくして、再結合による性能劣化を防止することができるようになる。
【００３４】
【効果】
以上、本発明は、裏面電極上に形成されたｐ型化合物半導体からなる光吸収層の上にヘテロ接合のためのｎ型のバッファ層を設けてなる化合物薄膜太陽電池の製造方法にあって、硫化亜鉛ＺｎＳＯ４、チオ尿素ＣＳ（ＮＨ２）２、アンモニアＮＨ４ＯＨの３液混合水溶液を用いてＣＢＤ法によりバッファ層を形成するに際して、その３液混合水溶液に光吸収層を浸して成膜の反応が進むにしたがってＺｎＳからＺｎＯの成分が生じやすくなるように水溶液の混合比を変えていく手段をとるようにしたもので、接合性の良い特性の安定したｐｎ接合を得ることができるとともに、透明電極との間の障壁をなくして再結合による性能劣化を防止することができるという利点を有している。
【００３５】
また、本発明は、裏面電極上に形成されたｐ型化合物半導体からなる光吸収層の上にヘテロ接合のためのｎ型のバッファ層を設けてなる化合物薄膜太陽電池において、下部の光吸収層から上部の透明電極へ向かって成分の割合がＺｎＳからＺｎＯに連続的または段階的に変化するバッファ層を設けるようにしたもので、接合性の良い特性の安定したｐｎ接合を得ることができるとともに、透明電極との間の障壁をなくして再結合による性能劣化を防止することができるという利点を有している。
【図面の簡単な説明】
【図１】一般的な化合物半導体による薄膜太陽電池の基本的な構造を示す正断面図である。
【図２】本発明によってＳＬＧ基板上に裏面電極および光吸収層を形成するまでの製造過程の一例を示す図である。
【図３】本発明によって光吸収層上にバッファ層および透明電極を形成するまでの製造過程を示す図である。
【図４】本発明によってＳＬＧ基板上に拡散制御層、裏面電極、アルカリ層および積層プリカーサを形成するまでの製造過程を示す図である。
【図５】本発明によってＳＬＧ基板上に拡散制御層を介して光吸収層、バッファ層および透明電極を形成するまでの製造過程を示す図である。
【符号の説明】
１　ＳＬＧ基板
２　Ｍｏ電極
５　光吸収層
６　バッファ層
７　透明電極[0001]
[Industrial applications]
The present invention relates to a compound thin-film solar cell in which an n-type buffer layer for heterojunction is provided on a light-absorbing layer made of a p-type compound semiconductor formed on a back electrode, and a method of manufacturing the same.
[0002]
[Prior art]
FIG. 1 shows a basic structure of a thin film solar cell using a general compound semiconductor. That is, a Mo electrode 2 serving as a back electrode (positive electrode) is formed on an SLG (soda lime glass) substrate 1, a p-type light absorbing layer 5 is formed on the Mo electrode 2, and the light absorbing layer is formed. A transparent electrode (minus electrode) 7 is formed on 5 via an n-type buffer layer 6 for heterojunction.
[0003]
As the light absorbing layer 5 in the thin film solar cell using the compound semiconductor, a group I-III-VI group II based on Cu, (In, Ga), or Se can be used as a material capable of obtaining a high energy conversion efficiency exceeding 18% at present. A CIGS thin film of Cu (In + Ga) Se2 is used.
[0004]
Conventionally, as a buffer layer in this type of compound thin film solar cell, a CdS film, which is a II-VI compound semiconductor, is chemically grown from a solution by CBD (Chemical Bath Deposition) to optimize the CIS light absorbing layer. (See US Pat. No. 4,610,091).
[0005]
Conventionally, a ZnS film is formed by a CBD method as a buffer layer capable of obtaining a high-conversion-efficiency hetero-bond that does not contain harmful substance Cd (see JP-A-8-330614). ).
[0006]
[Problems to be solved by the invention]
The problem to be solved is that, in the conventional compound thin film solar cell, since the composition of the light absorption layer, which is a p-type compound semiconductor, and the buffer layer, which is an n-type semiconductor, are completely different, defects are likely to occur in the junction. It is becoming.
[0007]
Further, when the buffer layer is formed by the CBD method, when the light absorption layer is immersed in the solution, the diffusion of the Zn or Cd component into the light absorption layer and the film formation of ZnS or CdS proceed simultaneously, so that the light absorption layer There is a problem that the characteristics tend to vary depending on the crystallinity and the surface state.
[0008]
[Means for Solving the Problems]
The present invention relates to a method for manufacturing a compound thin-film solar cell in which an n-type buffer layer for heterojunction is provided on a light-absorbing layer made of a p-type compound semiconductor formed on a back electrode, When forming a buffer layer by a CBD method using a three-component mixed aqueous solution of ZnSO4, thiourea CS (NH2) 2, and ammonia NH4OH, in order to obtain a stable pn junction having good junction characteristics, The light absorbing layer is immersed in the three-liquid mixed aqueous solution, and a processing means is employed in which the mixing ratio of the aqueous solution is changed so that the component of ZnO is easily generated from ZnS as the film forming reaction proceeds.
[0009]
The present invention also provides a compound thin film solar cell comprising an n-type buffer layer for heterojunction provided on a p-type compound semiconductor light-absorbing layer formed on a back electrode. A buffer layer is provided in which the ratio of the components changes continuously or stepwise from ZnS to ZnO from to the upper transparent electrode.
[0010]
【Example】
2 and 3 show a manufacturing process of the compound thin film solar cell.
[0011]
First, as shown in FIG. 2, a Mo electrode 2 as a back electrode is formed on an SLG (soda lime glass) substrate 1 by sputtering. Next, when the light absorption layer 5 of the CIGS thin film is formed on the Mo electrode 2, the In layer 32 is first formed by the first sputtering process SPT-1 using the In simple target T1, and then the In layer 32 is formed thereon. Then, a Cu-Ga alloy layer 31 is formed by a second sputtering process SPT-2 using a Cu-Ga alloy target T2 to form a laminated precursor 3 composed of the In layer 32 and the Cu-Ga alloy layer 31. I do. Then, in a heat treatment step HEAT, the laminated precursor 3 is heat-treated in a Se atmosphere to produce the light absorption layer 5 of the CIGS thin film.
[0012]
Thus, since the In layer 32 is provided on the Mo electrode 2 and the Cu—Ga alloy layer 31 is provided thereon to form the laminated precursor 3, the element at the interface with the Mo electrode 2 is formed. Can be suppressed from alloying due to solid layer diffusion. Then, when the laminated precursor 3 is heat-treated in a Se atmosphere to be selenized, the In component can be sufficiently diffused to the Mo electrode 2 side, and Ga having a low diffusion rate is present at the interface with the Mo electrode 2. The light absorption layer 5 of CIGS made of high quality P-type semiconductor Cu (In + Ga) Se2 with uniform crystal is formed without segregation to form a Cu-Ga-Se layer with poor crystallinity. be able to.
[0013]
Therefore, segregation of a different layer (Cu—Ga—Se layer) having poor crystallinity, structural brittleness, and conductivity at the interface with the Mo electrode 2 does not occur, and the adhesion with the Mo electrode 2 does not occur. It is possible to obtain a light absorbing layer of high quality which is structurally strong and has high quality and does not deteriorate the battery characteristics due to leakage between cells.
[0014]
Next, as shown in FIG. 3, an n-type buffer layer 6 is formed to form a heterojunction with the p-type light absorbing layer 5. Then, a transparent electrode 7 made of ZnO: Al, TCO or the like is formed on the buffer layer 6 by sputtering.
[0015]
4 and 5 show another manufacturing process of the compound thin film solar cell.
[0016]
In this case, at the time of heat treatment for selenization of the laminated precursor 3, the alkali layer 8 made of Na 2 S is formed on the Mo electrode 2 so that the Na component can be diffused into the light absorbing layer 5 to improve the photoelectric conversion efficiency. It is provided.
[0017]
The alkali layer 8 is formed by immersing the film-forming substrate of the Mo electrode 2 in an aqueous solution in which Na2S.9H2O (sodium sulfide nonahydrate) is dissolved in pure water at a weight concentration of 0.1 to 5% and spin-dried. After that, the film is formed by performing a baking process at 150 ° C. in the air for 60 minutes in order to adjust moisture remaining in the film.
[0018]
Then, between the SLG substrate 1 and the Mo electrode 2, a diffusion control layer 9 made of SiO2, Al2O3, or the like for controlling the diffusion of the Na component contained in the SLG substrate 1 into the light absorption layer 5 is formed by a CVD method. Like that.
[0019]
The present invention relates to a compound thin film solar cell having such a configuration, and particularly as a buffer layer 6, a component ratio is continuously or stepwise from ZnS to ZnO from a lower light absorbing layer 5 to an upper transparent electrode 7. The structure changes dynamically.
[0020]
In the present invention, when the buffer layer 6 is formed, a CBD method using a three-liquid mixed aqueous solution of zinc sulfide ZnSO 4, thiourea CS (NH 2) 2, and ammonia NH 4 OH is adopted, and the three-liquid mixed aqueous solution is mixed with light. A method is employed in which the mixing ratio of the aqueous solution is changed so that the surface of the absorption layer 5 is immersed and the components of ZnO are easily generated from ZnS as the film formation reaction proceeds.
[0021]
At this time, after the surface of the light absorbing layer 5 is immersed in a three-liquid mixed aqueous solution in which the amount of thiourea mixed is smaller than that of the other two liquids to form a film, the amount of zinc sulfide mixed in the aqueous solution is continuously adjusted. Alternatively, the film formation is continuously performed while increasing stepwise.
[0022]
During the film formation, the aqueous solution is heated to evaporate the ammonia.
[0023]
Normally, aqueous solutions of 0.16M_ZnSO4, 0.6M_CS (NH2) 2, and 7.5M_NH4OH are mixed in equal amounts, and the Mo electrode 2 and the light absorbing layer 5 are formed on the SLG substrate 1 in the three-liquid mixed aqueous solution. After charging the base material, the container is covered with a lid in order to suppress the volatilization of ammonia, and immersed for 30 to 120 minutes to form the buffer layer 6.
[0024]
On the other hand, in the present invention, when the substrate is put into the above-mentioned three-liquid mixed aqueous solution to form the buffer layer 6, the amount of thiourea is initially reduced and the film is formed while evaporating the ammonia. The three-solution mixed aqueous solution is changed continuously or stepwise so that Zn (OH) 2 is easily generated by adding ZnSO 4 to increase the supply source of Zn as the reaction proceeds. Like that.
[0025]
The specific formation of the buffer layer 6 by the CBD method is as follows.
[0026]
As a first stage treatment, aqueous solutions of 0.16M_ZnSO4, 0.6M_CS (NH2) 2, and 7.5M_NH4OH are mixed at a ratio of 240ml: 160ml: 240ml, and heated in a water bath at 80 ° C for 20 minutes. Then, the substrate is put into the three-liquid mixed aqueous solution, and a film is formed for 15 minutes.
[0027]
As the second-stage treatment, 3.68 g (80 ml in terms of 0.16 M) of ZnSO4.7H2O is added to the first-stage three-liquid mixed aqueous solution, and a film is formed for 15 minutes.
[0028]
As the third-stage treatment, 1.76 g of ZnSO4.7H2O is further added to the three-liquid mixed aqueous solution of the second stage, and a film is formed for 15 minutes.
[0029]
As the fourth stage treatment, 1.76 g of ZnSO4.7H2O is further added to the three-stage mixed aqueous solution of the third stage, and a film is formed for 15 minutes.
[0030]
As a fifth stage process, after performing film formation for a total of 60 minutes by the first to fourth stage processes, Zn (OH) 2 is dehydrated to obtain ZnO at a temperature of 100 to 300 ° C. in order to obtain ZnO. An annealing process for heating is performed for 30 to 300 minutes.
[0031]
During the film formation, the base is immersed in an open state without covering the container of the three-part mixed aqueous solution in order to volatilize the ammonia so that Zn (OH) 2 is more easily generated.
[0032]
First, as a chemical reaction by CBD,
ZnSO4 + xNH4OH → [Zn (NH3) x] 2 + SO4 2 + xH2O
ZnSO4 + 2NH4OH → Zn (OH) 2 ↓ + 2NH4 + SO4 2
A competitive reaction occurs. The ammine complex of Zn produced by this reaction reacts with thiourea to form ZnS, and the likelihood of the reaction is controlled by the concentration of ammonia (including pH) and the ratio of each component of the three-component aqueous solution. It is thought that it is possible.
[0033]
As described above, according to the present invention, the ratio of the components of the buffer layer 6 gradually changes from ZnS to ZnO from the lower light absorbing layer 5 to the upper transparent electrode 7. Therefore, it is possible to obtain a stable and high-quality pn junction with good bonding properties to the light absorbing layer 5. Then, the barrier between the transparent electrode 7 is eliminated, and the performance degradation due to the recombination can be prevented.
[0034]
【effect】
As described above, the present invention relates to a method for manufacturing a compound thin-film solar cell comprising an n-type buffer layer for heterojunction provided on a light-absorbing layer made of a p-type compound semiconductor formed on a back electrode. When a buffer layer is formed by a CBD method using a three-liquid mixed aqueous solution of zinc sulfide ZnSO4, thiourea CS (NH2) 2, and ammonia NH4OH, the light absorbing layer is immersed in the three-liquid mixed aqueous solution, and the film forming reaction proceeds. Means to change the mixing ratio of the aqueous solution so that the component of ZnO is easily generated from ZnS in accordance with the formula (1). A stable pn junction with good bonding properties can be obtained, and There is an advantage that the barrier between them can be eliminated and performance degradation due to recombination can be prevented.
[0035]
The present invention also provides a compound thin-film solar cell comprising an n-type buffer layer for heterojunction provided on a p-type compound semiconductor light-absorbing layer formed on a back electrode. A buffer layer in which the proportion of components changes continuously or stepwise from ZnS to ZnO from the top to the upper transparent electrode is provided, so that a stable pn junction with good junction characteristics can be obtained. In addition, there is an advantage that performance degradation due to recombination can be prevented by eliminating a barrier between the transparent electrode.
[Brief description of the drawings]
FIG. 1 is a front sectional view showing a basic structure of a thin film solar cell using a general compound semiconductor.
FIG. 2 is a diagram showing an example of a manufacturing process up to forming a back electrode and a light absorbing layer on an SLG substrate according to the present invention.
FIG. 3 is a view showing a manufacturing process until a buffer layer and a transparent electrode are formed on a light absorbing layer according to the present invention.
FIG. 4 is a diagram showing a manufacturing process up to the formation of a diffusion control layer, a back electrode, an alkali layer, and a laminated precursor on an SLG substrate according to the present invention.
FIG. 5 is a view showing a manufacturing process until a light absorption layer, a buffer layer, and a transparent electrode are formed on a SLG substrate via a diffusion control layer according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 SLG substrate 2 Mo electrode 5 Light absorption layer 6 Buffer layer 7 Transparent electrode

Claims (5)

裏面電極上に形成されたｐ型化合物半導体からなる光吸収層の上にヘテロ接合のためのｎ型のバッファ層を設けてなる化合物薄膜太陽電池の製造方法であって、硫化亜鉛ＺｎＳＯ４、チオ尿素ＣＳ（ＮＨ２）２、アンモニアＮＨ４ＯＨの３液混合水溶液を用いてＣＢＤ法によりバッファ層を形成するに際して、その３液混合水溶液に光吸収層を浸して成膜の反応が進むにしたがってＺｎＳからＺｎＯの成分が生じやすくなるように水溶液の混合比を変えていくようにしたことを特徴とする化合物薄膜太陽電池の製造方法。A method for manufacturing a compound thin-film solar cell in which an n-type buffer layer for heterojunction is provided on a light-absorbing layer made of a p-type compound semiconductor formed on a back electrode, comprising: zinc sulfide ZnSO4; When a buffer layer is formed by a CBD method using a three-component aqueous solution of CS (NH 2) 2 and ammonia NH 4 OH, a light absorbing layer is immersed in the three-component aqueous solution and ZnS is converted to ZnO as the film forming reaction proceeds. A method for producing a compound thin-film solar cell, wherein the mixing ratio of an aqueous solution is changed so that components are easily generated. チオ尿素の混入量が他の２液よりも少ない３液混合水溶液に光吸収層を浸して成膜を行わせたうえで、その水溶液における硫化亜鉛の混入量を連続的または段階的に増加させながら成膜を行わせるようにしたことを特徴とする請求項１の記載による化合物薄膜太陽電池の製造方法。The film is formed by immersing the light absorbing layer in a three-component mixed aqueous solution in which the amount of thiourea mixed is smaller than the other two solutions, and then the amount of zinc sulfide mixed in the aqueous solution is increased continuously or stepwise. 2. The method for manufacturing a compound thin film solar cell according to claim 1, wherein the film is formed while the film is formed. 成膜中、水溶液を加熱してアンモニアを蒸発させるようにしたことを特徴とする請求項１の記載による化合物薄膜太陽電池の製造方法。2. The method according to claim 1, wherein the aqueous solution is heated to evaporate the ammonia during the film formation. 成膜終了後に脱水のためのアニール処理を行うようにしたことを特徴とする請求項１の記載による化合物薄膜太陽電池の製造方法。2. The method according to claim 1, wherein an annealing process for dehydration is performed after the film formation is completed. 裏面電極上に形成されたｐ型化合物半導体からなる光吸収層の上にヘテロ接合のためのｎ型のバッファ層を設けてなる化合物薄膜太陽電池において、そのバッファ層が下部の光吸収層から上部の透明電極へ向かって成分の割合がＺｎＳからＺｎＯに連続的または段階的に変化するものであることを特徴とする化合物薄膜太陽電池。In a compound thin-film solar cell in which an n-type buffer layer for heterojunction is provided on a light-absorbing layer made of a p-type compound semiconductor formed on a back electrode, the buffer layer extends from a lower light-absorbing layer to an upper part. Wherein the proportion of the component changes continuously or stepwise from ZnS to ZnO toward the transparent electrode of (1).
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